This invention relates to delivering prostheses into the body.
Prostheses, such as stents, grafts and the like, are placed within the body to improve the function of a body lumen. For example, stents with substantial elasticity can be used to exert a radial force on a constricted portion of a lumen wall to open a lumen to near normal size.
These stents can be delivered into the lumen using a system which includes a catheter, with the stent supported near its distal end, and a sheath, positioned coaxially about the catheter and over the stent.
Once the stent is located at the constricted portion of the lumen, the sheath is removed to expose the stent, which is expanded so it contacts the lumen wall. The catheter is subsequently removed from the body by pulling it in the proximal direction, through the larger lumen diameter created by the expanded prosthesis, which is left in the body.
This invention provides smooth delivery and accurate positioning of prostheses in the body. In embodiments, systems are provided that include elongate members extending generally along the axis of a supporting catheter to a free ends. The elongate members extend through openings in the prosthesis to maintain the position of the prosthesis on the catheter. The prosthesis can be released from the catheter by relative axial motion of the catheter and the elongate members such that the free ends are removed from the openings in the prosthesis. In embodiments, the elongate members hold the distal end of a self-expanding stent at a desired axial location and in radial compaction as a restraining sheath is withdrawn. The friction between the sheath and stent puts the stent under tension, which reduces the radial force on the sheath wall, allowing smoother retraction. Proximal portions of the stent radially expand and axially shorten. The distal end, however, is maintained at the desired axial location and released from the catheter to contact the body lumen wall without substantial axial shortening.
In an aspect, the invention features a system for positioning a prosthesis in contact with tissue within a patient. The system includes a prosthesis having proximal and distal ends and a tissue-engaging body therebetween. The prosthesis has a radially compact form for delivery into the patient and is radially expandable along its body for engaging tissue. The length of the prosthesis varies in dependence on the expansion of the body. The system further includes a catheter having a portion for supporting the prosthesis in the compact form during delivery into the patient and constructed for expanding the prosthesis in contact with tissue. The portion includes a member positioned to engage the prosthesis near the distal end to maintain a corresponding portion of the prosthesis radially compact at a predetermined axial location, while proximal portions of the prosthesis are radially expanded to engage tissue. The portion of the prosthesis engaged by the member is releasable from the catheter at an axial location substantially corresponding to the predetermined location by relative axial motion between the member and the prosthesis, so the free end of the member disengages the prosthesis.
Embodiments may include one or more of the following features. The prosthesis has, near its distal end, an opening through the tissue-engaging body and the member extends generally along the axis of the catheter to a free end that engages the prostheses by extending through the opening and the portion of the prosthesis corresponding to the opening is released by axial motion so the free end of the member is removed from the opening. The opening may include a series of openings positioned around the circumference of the prosthesis and the member is a corresponding series of elongated members, which pass through the series of openings. The member extends distally to the free end so release of the prosthesis from the catheter is by moving the members proximally relative to the prosthesis. The member is fixed on the catheter so release of the prosthesis from the catheter is by moving the catheter relative to the prosthesis. The elongate member extends at an angle with respect to the axis of the catheter to form a predefined wedge space between the member and the catheter for engaging the prosthesis. The angle is about 3-8 degrees. The member is formed of a flexible material that deflects outwardly in response to a radial force, to release the free end of the member from the opening. The member is a superelastic wire. The length of the portion of the member passing through the opening is smaller than the expanded diameter of the prosthesis. The prosthesis is a tubular-form prosthesis positioned coaxially about the supporting portion of the catheter in the radially compact form. The prosthesis is formed of a patterned filament and the opening is formed by the pattern. The prosthesis is knitted and the opening is formed by knit-loops in the knit pattern. The opening is the end loop of the knit pattern. The prosthesis is self-expanding. Portions of the self-expanding prosthesis corresponding to the member are maintained in compact form by the member and portions remote from the member are maintained in compact form by a restraint. The restraint is an axially retractable sheath and the self-expanding prosthesis engages the sheath with substantial friction to place the prosthesis under tension as the sheath is retracted.
In another aspect, the invention features a system for positioning a prosthesis in contact with tissue on the wall of a lumen of a patient. The system includes a tubular prosthesis having a proximal and distal end and a tissue-engaging body therebetween. The prosthesis has a radially compact form for delivery into the patient and is radially expandable along its body for engaging tissue. The length of the prosthesis varies in dependence on expansion of the body. The prosthesis is formed of a patterned filament and includes a series of openings through the tissue-engaging body of the prosthesis about the circumference of the prosthesis, near the distal end. The system further includes a catheter having a portion for supporting the prosthesis coaxially about the portion in the compact form for delivery into the patient and constructed for expanding the prosthesis into contact with tissue. The portion includes a series of elongate members arranged about the circumference of the catheter, fixed to the catheter, and extending generally along the axis of the catheter to free ends positioned to pass through corresponding openings about the circumference of the tissue-engaging body of the prosthesis. The members maintain corresponding portions of the prosthesis radially compact at a predetermined axial location, while proximal portions of the prosthesis are radially expanded to engage tissue. The portion of the prosthesis corresponding to the openings is releasable from the catheter at an axial location substantially corresponding to the predetermined location by moving the catheter proximally so the free ends of the members are removed from the openings.
Embodiments may include one or more of the following features. The prosthesis is self-expanding and the elongate members in the openings maintain the distal end of the prosthesis compact after other portions of the prosthesis are radially expanded. The portions of the prosthesis proximal of the members are maintained compact by a retractable sheath. The prosthesis engages the sheath with substantial friction to place the prosthesis under tension as the sheath is retracted. The elongate members are formed of superelastic metal wires. The elongate members are formed of a flexible material that deflects outwardly in response to a radial force of expansion of the prosthesis to release the free ends of the members from the openings. The length of the portions of the elongated strands passing through the loops is smaller than the expanded diameter of the prosthesis. The elongated strands extend at an angle with respect to the axis of the catheter. The angle is about 3-8 degrees.
In another aspect, the invention features a system for positioning a self-expanding prosthesis in the body. The system includes a self-expanding prosthesis having a proximal end and a distal end and a tissue-engaging body therebetween. A catheter is provided having a portion supporting a prosthesis in a radially compact form. The portion of the catheter supporting the prosthesis includes a member positioned to engage the distal end of the prosthesis to maintain corresponding portions of the prosthesis compact at a predetermined axial location with respect to the catheter while other portions of the prosthesis are radially expanded to engage tissue. The system includes a retractable sheath positioned over and in contact with the prosthesis when the prosthesis is in the compact form. A tensioning element applies an axial force to the prosthesis to reduce frictional force between the sheath and the prosthesis while retracting the sheath to expose the prosthesis.
The sheath may be a restraining sheath that maintains portions of the prosthesis compact against the radial expansion force of the prosthesis and the tensioning element is formed by the sheath, engaged by the prosthesis with substantial frictional force to place the prosthesis under tension as the sheath is retracted.
In another aspect, the invention features methods of positioning a prosthesis in the body. For example, the method may include providing a system as described above, positioning the system in a body lumen with the distal end of the prosthesis in the compact form located substantially adjacent the axial location of the lumen wall corresponding to the desired distal extension of the prosthesis, expanding portions of the prosthesis proximal of the distal end to engage the wall of the lumen, and withdrawing the catheter proximally so the distal end is disengaged from the catheter and expanded against the lumen wall. The prosthesis may be positioned at a location adjacent a side duct branching from the lumen. The body lumen may be the bile duct. Many methods are evident from the description herein.
The advantages of the invention are numerous. For example, systems of the invention can provide accurate positioning of a prosthesis, even a self-expanding stent which changes its axial length upon expansion. Accurate positioning of the prosthesis is particularly important in cases where the portion of the body lumen to be treated is adjacent a tissue feature, such as another body lumen, that should not be occluded by the prosthesis. A tumor in the bile duct that is located adjacent the duodenum is one example. It is desirable to center the prosthesis about the tumor, but care must be taken so that the end of the prosthesis does not extend beyond the duodenum. Otherwise the motion of the body and the flow of food particles may drag the stent from the bile duct.
Further features and advantages follow.